This Bose® 901 Series II Active Equalizer, serial number 46234, came in for a repair just recently. As is happening with nearly all of these early ’70s equalizers by now, this one had developed poor sound quality and distortion and was due for an overhaul.

This one received all new resistors, electrolytic and film capacitors, and upgraded output capacitors and silver solder. The transistors were also hand-matched to ensure equal balance and curve precision.

Really good question. Beyond my knowledge right now to design a PCB unfortunately. I can’t imagine it would be that tough though. I imagine it’d probably cost a couple thousand bucks of an engineer’s labor to make me some Gerbers, but then only a few bucks a board.